Triple score pressure relief system for an aerosol container

ABSTRACT

A two or three piece metal container is adapted to hold a pressurized product for dispensing through a valve mounted on the container. The container has a safety venting system therein, whereby the product may be vented from a filled pressurized container through the system when an increase in internal pressure threatens to blow the top or bottom off the container. The venting system comprises a plurality of triple scores formed in the seam where the container body is joined to the top closure of the container. When the internal pressure of a filled container increases sufficiently, the periphery of the top closure buckles outwardly causing the residual of the main score in the triple score to fracture and thus produce a plurality of vents to permit the highly pressurized contents of the sealed container to safely escape and prevent end blow-off.

United States Patent [191 Kinkel [451 Nov. 26, 1974 TRIPLE SCOREPRESSURE RELIEF SYSTEM FOR AN AEROSOL CONTAINER Primary E.raminer.l0hnPetrakes Attorney, Agent, or FirmRobert P. Auber; George P,

[75] Inventor: Christian Frederick Kinkel, Ziehmer Prospect Heights,Ill.

[73] Assignee: American Can Company,

Greenwich, Conn. [57] ABSTRACT [22] Filed: May 7, 1973 A two or threepiece metal container is adapted to hold a pressurized product fordispensing through a pp N05 357,606 valve mounted on the container. Thecontainer has a safety venting system therein, whereby the product 52us. CI. 220/89 A, 220/44 R 222/397 may he vented hem e filledPressurized Container 51 lm. Cl 865d 83/14, 1305b 7/32 through theSystem Wheh eh htereeee ht ihtethel P 58 Field of Search 220/44 R, 89 A67" Sure threatens to blew the top or bottom Off the 222/397 tainer. Theventing system comprises a plurality of triple scores formed in the seamwhere the container [56] References Cited body is joined to the topclosure of the container.

When the internal pressure of a filled container in- UNITED STATESPATENTS creases sufficiently, the periphery of the top closure 5336919012/1943 LO Y iZO/gg A buckles outwardly causing the residual of the mainscore in the triple score to fracture and thus produce H1965 gfig g222/397 a plurality of vents to permit the highly pressurized g 12/1966y contents of the sealed container to safely escape and 3:450:3Q5 19 9prevent end blOW-Off.

3.680.743 8/1972 Reinnagel 222/397 3,786,967 1/1973 Giocomo et al.222/397 2] 11 Clam, 9 Drawlhg Flgures l I l l L a a -1 TRIPLE SCOREPRESSURE RELIEF SYSTEM FOR AN AEROSOL CONTAINER BACKGROUND OF THEINVENTION The present invention relates generally to a metal aerosolcontainer having a pressure relief system whereby the internal contentsof the container may be vented therefrom when the internal pressurerises sufficiently to a level threatening blowing the top or bottom endoff the container. More particularly this invention relates to a two orthree piece metal aerosol container having a simple venting system toeliminate explosion of a filled aerosol container when the internalpressure rises considerably, which may be encountered during excessiveheating of the container.

For many years pressurized aerosol containers have been marketed to thegeneral public. These containers usually comprise a three piece metalcontainer having therein a product to be dispensed, together with apropellant that provides the internal pressure necessary to dispense theproduct through a valve mounted on the container. Products such asfoods, cosmetics, insecticides, etc. have been packaged in these typesof containers with considerable success.

However, due to the fact that the container is pressurized, problemshave been encountered when the internal pressure of the container risesrapidly above that pressure to which the container construction has thecapacity to hold. In some instances this rapid increase in internalpressure, resulting from rapid heating, has

caused the container to explode. This has sometimes occurred inwarehouse fires where large quantities of these aerosol containers arestored. In some cases, firemen have been injured during such explosionsand in some instances firemen are unable to control the flames sincethey cannot approach them. Over the years many attempts have been madeto design containers having pressure relief systems in order toeliminate the possible explosive danger from pressurized aerosolcontainers. Many of these constructions include specialized valves whichrupture upon heating or when exposed to extremely high internalcontainer pressures. However, in general, such constructions havegreatly increased the cost of these containers to such a degree thatthey are not economically practical.

Other safety features have included weak areas in the container bodysuch that under excessive internal pressure the weakened portion wouldrupture and permit venting of the container contents. One suchconstruction is shown in US. Pat. No. 3,074,602. In this patent apressure sensitive area is formed in the valve cup such that when thedome of the container everts or buckles due to high internal pressure,venting will occur through a rupture produced in the pressure sensitivearea. However positioned, this weakened portion would not necessarilyrupture when the dome of the container buckles and venting through thesingle area of failure would not necessarily be rapid enough to preventexplosion of the container.

In US. Pat. No. 2,795,350 (Lapin), a nick is formed in the periphery ofthe body closure of the container where it forms a double seam withthecontainer body. In this two piece aerosol container extremely highpressure supposedly causes the concave bottom wall to buckle and rupturethe nick to form a vent through the bottom of the container. However. inthe usual case the bottom would not buckle uniformly and-should thebuckling begin to occur opposite the nick, no relief vent would beformed until the full bottom of the container would blow off. Moreover,a single nick would not provide an adequate venting rate.

The prior art more recently has witnessed an improvement over Lapinwherein a multiplicity of single scores are employed in the upper doubleseam where the tubular container body is joined to the domed topclosure. This latest safety feature protects against can failures in thepacking and marketing of aerosol cans. If excessive internal pressuredevelops in a filled can due to an unusual situation, the safety featureactivates rapidly and provides adequate venting to completely vent thecontainer contents before the container fails explosively.

Full cans will vent if excessive pressure develops in the can due tomisuse. This might involve placing the can on a hot stove or radiator,near a hot iron, or in the glove box, trunk, or window of a car sittingout in the sun.

Generally, partially filled cans will also vent under the conditionsmentioned above; however, near-empty cans may fail at the side seam intypical three piece metal cans before the pressure required to activatethe safety feature is generated under prolonged exposure to intenseheat.

Aerosol cans which are considered empty or nearly empty usually containsa small amount of residual product and propellant. These small amountsare sometimes not sufficient to generate the pressure needed to activatethe safety feature when the can is incinerated. Under the intenseheat ofincineration, some of these cans will vent or rupture at the side seamof a three piece can. This is due to the fact that the side seam isadhered with a solder or relatively low temperature material. This sideseam rupture will occur at pressures below the pressure required tobuckle the top closure and thus form the safety venting feature. Thisfailure, although dangerous, is less violent than blow-off of the top orbottom end.

Certain products in cans which are thrown away as empty or nearly emptywill generate sufficient pressure to activate the safety feature whenincinerated. This is entirely dependent upon the amount and type ofproduct and propellant remaining in the can. Full or partially full canswill also vent safely if they are incinerated.

As is well-known, there is some controversy in the usage of aerosolcontainers due to the fact that they are under high internal pressuresand subject to abusive use. To date, the various concepts for pressurerelieving an aerosol container have proved uneconomical. Any reliefconcept must function under both normal use conditions and underuncontrollable use conditions which violate general precautionarylabeling. Such abusive conditions include storage in direct sunlight,storage in enclosed automobiles during summer months and warehousefires.

Also, the relief concept must allow function of the container undercontrollable use conditions in violation of precautionary labeling solong as the temperature does not exceed 250 F for approximately onehour. At temperatures below 250 F, the time of exposure can besignificantly increased.

The greatest danger, when three-piece aerosol containers are subject totemperature abuse, is that the bottom of the container may evert orbuckle under extreme internal pressure and blow off. Due to the factthat the bottom is constructed to withstand extreme internal pressures,when these pressures are reached, the bottom end may buckle and separatefrom the remainder of the container, possibly resulting in propellingparts of the container about the immediate area.

A secondary type of failure encountered when internal pressure increasesover the maximum allowable by the three-piece container construction isa side seam rupture, described above, which generally results fromexposure to high temperatures. The side seam failure is dependent uponexposure temperature, the position of the container with respect to theheat source, the type of product and propellant packed in the container,the quantity of product and propellant remaining in the container, andthe container size. For a container of average size, such as those of 3inches in diameter and approximately 7 9/16 inches in height, it hasbeen found that the relief mechanism must be capable of releasing l4cubic feet per minute of internal gas at 200 psig. Less release capacityis required for smaller containers as vent capacity is strictlydependent upon volumetric capacity.

Although a plurality of single scores, as described above, function wellas a venting mechanism, their consistency of performance is not deemedhigh enough for commercial standards. High score residuals are requiredto prevent premature fracturing, especially during manufacture(subsequent forming and double seaming operations), while low scoreresiduals are required for adequate venting. However, if the scoreresidual is too low, the score is likely to fracture prematurely, and ifthe score residual is too high, the score is likely to either not openat all, or open insufficiently to provide an adequate venting rate toprevent explosive failure of the container. The difference between themaximum possible score residual and the minimum possible score residualis called the working range. As large a working range as possible ispreferred to allow for numerous variations in manufacture.

Using the multiplicity of single scores, it was found that inconsistentand poor venting of the aerosol containers was due to variations in thelots of material to be used for end closures, as well as other factors.It was learned that the working ranges for various materials varied, andthat the working range for single scores in any given material was verynarrow. When a variety of materials were to be processed on one line ofproduction, the effective working range for manufacturing purposes wasfurther reduced because the effective minimum possible score residualthat could be used on the production line would correspond to thehighest of the various minimum score residuals of the various materialsand the effective maximum possible score residual that could be usedwould correspond to the lowest of the various maximum score residuals ofthe various materials. Since a manufacturing line handles variousmaterials, it is constrained according to the effective working range,which for single scores turns out to be very narrow, thus leaving littleroom for variation or error in manufacture. It is this narrow workingrange that causes the plurality of single scores to bend lessconsistently than is required commercially.

Accordingly, it was determined that a means of expanding the workingrange of score residuals was necessary to provide scores that would notfracture prematurely and yet would provide adequate ventingconsistently. It was unexpectedly discovered that the use ofanti-fracture scores oneither side of the main single score expanded theworking range by lowering the minimum possible score residual andraising the maximum possible score residual, thereby preventingpremature fracture to a greater extent, improving venting and permittingthe use of a wide range of plate tempers.

SUMMARY OF THE INVENTION Accordingly, the instant invention provides animprovement for safely venting excessive internal pressure in apressurized aerosol dispenser container having a tubular body closed atone end and a metal end wall closing the other end, the end wall beingsecured to the tubular body by an annular convoluted seam, comprising: aplurality of venting scores, and an anti-fracture score flanking eachside of each of said venting scores, said venting and anti-fracturescores penetrating partially through the metal of the end wall andextending from at least a portion of the most interior layer of the seamto the top portion of the seam, whereby when the internal pressurewithin the container increases and threatens to cause rupture of saidcontainer, the end wall will buckle outwardly causing the residual ofsaid venting scores to fracture to thereby produce a plurality of ventsto permit the pressurized contents to escape safely therethrough.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of athree-piece metal container utilized to dispense pressurized products.

FIG. 2 is a top plan view of the container of FIG. 1.

FIG. 3 is an enlarged, partial, sectional view showing the periphery ofthe dome and the container body prior to their being seamed together informing of the container.

FIG. 4 is an enlarged, sectional view taken substantially along the line4-4 in FIG. 3.

FIG. 5 is an enlarged, fragmentary, sectional view of the double seamformed by the periphery of the dome and the top of the container body.

FIG. 6 is an enlarged, fragmentary, side elevational view of the seamshown in FIG. 5 more fully illustrating the triple score.

FIG. 7 is an enlarged, partial, section view similar to FIG. 5 butillustrating the vent score on the interior of the periphery of thedome.

FIG. 8 is an enlarged, fragmentary, sectional view illustrating theperiphery of the dome after high internal pressure has buckled the headand fractured the vent score to form a safety pressure relief vent.

FIG. 9 is an enlarged, fragmentary, side elevational view illustratingthe ruptured score after buckling of the dome.

DESCRIPTION OF THE PREFERRED EMBODIMENT As a preferred or exemplaryembodiment of the instant invention FIGS. 1 and 2.show a container,generally designated 12, comprising a tubular metal body 14 having aside seam 15. The side seam 15 is generally sealed with solder, as iswell known in the art, although it may also be welded. Closing thebottom of the container is an end 16 hermetically seamed to the bottomof the body 14 by a seam 18.

As the container 12 will ultimately be utilized as an aerosol container,a dome 20 is seamed to the top of the body 12 by an annular, convoluted,double seam (five layers of interfolded material) 22. The upper end ofthe dome 20 has an orifice 23 defined by a top curl 24. After fillingwith product and a suitable propellant, a valve cup, not shown, isplaced into the orifice 23 and a suitable dispensing valve, also notshown, is positioned within the valve cup to seal the container 12 andto permit dispensing of the product and propellant from the container12.

A plurality of radial venting scores 26 are formed, preferably with ascoring punch when the dome 20 is flat, in the periphery of the dome 20in the area that is to be the top of the double seam 22. As may be seenbetter in FIGS. 3-6, the scores 26 are narrow grooves formed in theperiphery of the dome 20 and penetrate only partially through the metalof the dome 20. For example, a score 26 has a depth of approximately0.009 inch for a total metal thickness of 0.014 inch, leaving asolid-metal residual 30 of 0.005 inch. The developed length of the scoreis approximately 0.125 inch. As shown in FIG. 4 the included angle ofthe venting score 26 is approximately 60 and it is desirable that thisangle not be below 40. As will be noted the bottom 28 of the ventingscore 26 is essentially flat in cross sectional appearance. Thisprovides greater integrity and prevents premature cracking through theresidual 30 of the material which would result in leakage of product andpropellant from the container 12.

As illustrated in FIGS. 2, 4, 6 and 9, each of the venting scores 26 isflanked by a pair of shallower antifracture scores 27 having a depth ofapproximately 0.005 inch for the total metal thickness of 0.014 inch,leaving a solid metal residual 31 of 0.009 inch. The most effectivedifferential in score depths irrespective of the score depths is on theorder of about 3 mils. The developed length of the antifracture scores27 is about the same as the developed length of the venting score 26,approximately 0.125 inch. As shown in FIG. 4, the included angle of theanti-fracture scores 27 is approximately 70 and it is desirable thatthis angle not be less than 40. As can be seen in FIG. 4, the bottom 33of the anti-fracture scores 27 is essentially flat. The center-tocenterspacing between the vent score 26 and each of the anti-fracture scoresis approximately 60 mils, with a preferred range being between 50 and 70mils.

As can be seen in FIG. 3, the dome 20, prior to double seaming, has acorrugation 34 adjacent the seam area connecting the top of the body 14with the dome 20. The location of the venting score 26 is critical tothe consistency of venting. The venting score 26 must extend from atleast a portion of the most interior layer which fits within a curl 38which forms the peripheral edge of the dome 20. In forming the annular,convoluted double seam 22, the flange 36 is interfolded with the curl 38to hermetically seal and close the container 12 as the double seam 22 isformed. In addition, a small amount of sealing compound 40 is positionedalong the interior wall of the curl 38 to provide a hermetic seal informing the double seam 22. A similar type of double seam may be used toform the seam 18 at the bottom of the container 12.

The fully formed double seam 22, shown in FIG. 5, thus hermeticallyseals the dome to the body 14. Spaced about the top of the double seam22 are a plurality of venting scores 26 flanked by a pair ofantifracture scores 27, all of which extend radially within the top ofthe double seam 22.

32 of the seam 22 to the top portion of the seam 22. It

In a modified construction, shown in FIG. 7, a plurality of radialventing scores 42 and anti-fracture scores (not shown) are formed on theinterior of the periphery of the dome 20. Thus, when the double seam 22is formed by the flange 36 and curl 38, the scores are hidden by beingentirely within the double seam 22. In certain instances this hasaesthetic advantages in that the multiplicity of scores are not seen bythe user as are the exterior scores. However, either type of scoringwill function in the manner described hereinafter to provide a pressurerelief system for a filled container 12.

It can be seen in FIGS. 8 and 9 that when the internal containerpressure increases sufficiently the dome 20 buckles and the corrugation34 also deforms as the double seam 22 partially unfolds, raising theradial venting score 26 (and anti-fracture score 27) away from the seamand rupturing it to form a vent 44. This vent 44 permits pressurizedproduct and propellant from within the container 12 to escape and safelyvent the container. The anti-fracture scores 27 do not open to form anyvents.

As may be seen from the drawings, a plurality of radial venting scores26 have been formed in the double seam 22. This is to insure that nomatter where the dome 20 begins buckling due to increased internalpressure, a vent 44 will be formed almost immediately and as thebuckling continues about the periphery of the dome 20 additional vents44 will form about the periphery of the dome 20 as additional radialventing scores 26 are deformed and fractured.

It has been found that at 200 psig inside a 300 X 709 (3 inch diam, 79/16 inch height) can, 12 radial venting scores will vent from 14 to21.5 cubic feet per minute of gas. Eight radial venting scores per endwill vent from 1 1.5 to 14 cubic feet per minute of gas, and six radialventing scores per end will vent from 10 to 12.5 cubic feet per minuteof gas. In these tests air temperature was about 78 F. Thus, it can beseen for a container of such size a minimum of eight venting scores willpermit reasonably safe evacuation of the internal gases within anoverpressurized filled container, al-

though at least 12 score vents are preferred for greater reliability.

It must be noted that these tests were all conducted with filledcontainers containing sufficient amounts of GRAPH 1 STEEL TYPE w to meltthe conventional solder side seam so that failure could occur at theside seam rather than by buckling the dome 20 to form the vents 44. Butfailure of the side seam is far less serious than explosive failure atthe bottom or top where blow off could cause serious damage if containerparts are propelled about the area.

Experiments were conducted to evaluate the contribution of theanti-fracture scores. A multiplicity of single venting scores werecompared with a multiplicity of triple scores (venting score plus twoanti-fracture scores) on two different diameter cans, 202 (2 2/16"ENTING RATE (CFM) inch) and 207.5 (2 /32 inch) using two differentsteel plates for the end wall that isdesigned to buckle under excessivepressure. One steel, designated W, had not been successful with singlescores because of poor venting rates. The other steel, designated G, hada problem with the scores leaking. For successful commercial runs, it isnecessary to use both types of steel plate, which represent differenttempers, T3 and T4. It became apparent that different score residualswere required for different steels if only single scores were employed.It is strongly desirable that a single score resid ual be used fordifferent steels so that scoring equipment does not have to be changedevery time a different steel is run.

Accordingly, the experimental objective was to de- SCORE RESIDUAL (MILS)fine, with the use of graphs, the maximum possible score residual atwhich score fracture would occur after seaming the end to the can bodyto give commercially consistent venting, and the minimum possible TRIPLESCORE MIN. RESIDUAL score residual which would not fracture prematurely,for both single and triple scores for the two different steel plates.

SINGLE SCORE MIN. RESIDUAL- VENTING RATE (CFM) ture of the various typesof metals.

The two graphs below of vent rate versus score residual for a givenventing score illustrate a set of vent rate curves for 202 diameterends. The table following sum- 3 RE$IDUAP marizes pertinent data for 202and 207.5 diameter TABLE 207.5 DIAMETER Steel Type W Steel Type GMaximum Score Residual for 0.l25 CFM Vent Rate Single Score .0045".0053" Triple Score .0054 .0055" Minimum Score Residual Single Score.0033" .0042" Triple Score .0027" .0032" Working-Range Single Score.00l2" .0011" Triple Score .0027" .0023" Steel Type G T 202 DIAMETERSingle Score 036" Triple Score 0046" Minimum Score Residual Single ScoreTriple Score less than .0034" Working Range Single Score .0001" TripleScore greater than .0012" Maximum Score Residual for 0.125 CFM Vent Rate.0040 less than .0036" .0005" greater than .0016" The graphs and tableshow that the score residual which will permit a venting score to opensufficiently to give a vent rate of 0.125 c.f.m., a commerciallyfeasible venting rate, is always higher for triple scores than forsingle scores. It appears that the anti-fracture scores permit theventing scores to open to a greater extent. In other words, using triplescores enables the use of higher score residuals.

Furthermore, it can be seen that lower score residuals can be used withtriple scores without premature fracture. This would seem due to certainstrain reliefs provided by the anti-fracture scores. The net result isthat with triple scores the working range is significantly increased,the table indicating increases from 100 to greater than 1000 per cent.

It can be seen from the above data that the antifracture scores make asubstantial contribution to the success of manufacturing an end havingventing scores in at least the following five areas:

1. Enables the use of higher residuals, significantly increasing thesafety factor with respect to premature fracturing. 2. Permits a widerworking range. 3. Is less sensitive to normal plate property variations,and permits the use of plate which could not be used with single scores.

4. Allows the commercial production of scored ends within normalmanufacturing tolerances (i.e. plate and residual variations) whichwould be very difficult to produce with single scores only.

5. Permits ends made from different materials to be scored with the sametooling setup on one production line.

It is thought that the invention and many of its attendant advantageswill be understood from the foregoing description and it will beapparent that various changes may be madein the form, construction andarrangement of the parts without departing from the spirit and scope ofthe invention or sacrificing all of its material advantages, the formhereinbefore described being merely a preferred embodiment thereof.

What is claimed is:

1. In a pressurized aerosol dispenser container having a tubular bodyclosed at one end and a metal end wall closing the other end, the endwall being secured to the tubular body by an annular convoluted seam,the improvement for safely venting excessive internal pressure,comprising: a plurality of venting scores, and an anti-fracture scoreflanking each side of each of said venting scores, said venting andanti-fracture scores penetrating partially through the metal of the endwall and extending from at least a portion of the most interior layer ofthe seam to the top portion of the seam, whereby when the internalpressure within the container increases and threatens to cause ruptureof said container, the end wall will buckle outwardly causing theresidual of said venting scores to fracture to thereby produce aplurality of vents to permit the pressurized contents to escape safelytherethrough.

2. The improvement of claim 1 wherein the tubular body is metal and theanti-fracture scores are shallower than the venting score.

3. The improvement of claim 2 wherein the closed end is formed by aseparate end double seamed to the tubular body.

4. The improvement of claim 3 wherein the scores extend radially acrossthe end wall.

5. The improvement of claim 4 wherein the closed end is concave.

6. The improvement of claim 5 wherein the scores are located on theinterior of the metal end wall.

7. The improvement of claim 5 wherein the end wall is domed.

8. The improvement of claim 1 wherein the centerto-center spacingbetween the venting score and the anti-fracture scores is between 50 andmils.

9. The improvement of claim 8 wherein the spacing is 60 mils.

10. The improvement of claim 9 wherein the difference in depth betweenthe venting and anti-fracture scores is on the order of about 3 mils.

11. The improvement of claim 8 wherein the residual of the venting scoreis between 4 to 6 mils, and the residual of the anti-fracture scores isbetween 6 to 9 mils.

1. In a pressurized aerosol dispenser container having a tubular bodyclosed at one end and a metal end wall closing the other end, the endwall being secured to the tubular body by an annular convoluted seam,the improvement for safely venting excessive internal pressure,comprising: a plurality of venting scores, and an anti-fracture scoreflanking each side of each of said venting scores, said venting andanti-fracture scores penetrating partially through the metal of the endwall and extending from at least a portion of the most interior layer ofthe seam to the top portion of the seam, whereby when the internalpressure within the container increases and threatens to cause ruptureof said containeR, the end wall will buckle outwardly causing theresidual of said venting scores to fracture to thereby produce aplurality of vents to permit the pressurized contents to escape safelytherethrough.
 2. The improvement of claim 1 wherein the tubular body ismetal and the anti-fracture scores are shallower than the venting score.3. The improvement of claim 2 wherein the closed end is formed by aseparate end double seamed to the tubular body.
 4. The improvement ofclaim 3 wherein the scores extend radially across the end wall.
 5. Theimprovement of claim 4 wherein the closed end is concave.
 6. Theimprovement of claim 5 wherein the scores are located on the interior ofthe metal end wall.
 7. The improvement of claim 5 wherein the end wallis domed.
 8. The improvement of claim 1 wherein the center-to-centerspacing between the venting score and the anti-fracture scores isbetween 50 and 70 mils.
 9. The improvement of claim 8 wherein thespacing is 60 mils.
 10. The improvement of claim 9 wherein thedifference in depth between the venting and anti-fracture scores is onthe order of about 3 mils.
 11. The improvement of claim 8 wherein theresidual of the venting score is between 4 to 6 mils, and the residualof the anti-fracture scores is between 6 to 9 mils.